1. Field of the Invention
The present invention relates to solid state imaging devices carrying color filters on a top surface of light-receiving sections formed, and manufacturing method thereof.
2. Description of The Related Prior Art
Conventional ways for manufacturing color filters have been dyeing, printing, electro-plating or the like. Dyeing has been widely used, due to its high resolution on color filter patterns and its dyestuff which facilitate attaining a desired photospectrograph. There are two different methods to mount the color filters on the solid state imaging device: an on-wafer method and a filter bonding method. In particular, the on-wafer method, which enables the color filters to be mounted directly on a substrate of the solid state imaging device, has been considered as the mainstream in the field. Keeping these points in mind, combination of the dyeing method and the on-wafer method as mentioned above (referred to hereinafter as the on-wafer dyeing method) is used to form the solid state imagining device with color imaging function.
A description is given below of the solid state imaging device and the manufacturing method thereof featuring the on-wafer dyeing method, with reference of accompanying drawings.
FIG. 33 shows the structure of a prior art solid state imaging device. On a surface of a semiconductor substrate 1, an array of photodiodes or light-receiving sections 2 are arranged at given positions. An insulating layer, transfer electrodes and light-shielding layers are formed on each of transfer sections in the area of the surface of the semiconductor substrate 1 excluding the light receiving sections 2. The surface of the semiconductor substrate 1 is covered with a protecting layer 5. A transparent flattening layer 6 is formed to cover the whole protecting layer 5. Thereafter, color filters 7 are formed. The color filters 7 consists of three different colors: red color filters 7R, green color filters 7G and blue color filters 7B. Bonding pads 3 and scribe lines 4 are formed at an edge portion of the semiconductor substrate 1 of the solid state imaging device.
In forming the color filters 7, the material which is made by combining natural protein such as gelatin or casein and dichromate as a photo-sensitizer with water as a solvent, is evenly applied on the surface of the transparent flattening layer 6 mounted on the protecting layer 5, and then, ultraviolet rays are radiated via desired masks on the material. The unirradiated areas against the ultraviolet rays is dissolved into water to create color filter patterns. Then, the color filter patterns are colored with the dyestuffs containing a desired photospectrography to form the color filter 7. Finally, it is followed by the removal of the transparent flattening layer 6 disposed on the bonding pads 3 and the scribe lines 4 which are used for external line connection of the solid state imaging device. Through all the processes described above, color filters are completed.
In keeping with downsizing of chip size and higher number of pixels, it is generally required to reduce the size of the light-receiving sections included in the solid state imaging device. To achieve this, the color filters 7 need to be minimized. In this instance, it is necessary to make uniform the shape and the photo spectrography of the color filters 7. However, the material made by combining natural protein such as gelatin or casein with dichromate as photo sensitizer, which have been so far employed for the color filters, have a low resolution of patterning. Therefore, it makes the quality of the solid state imaging device carrying the color filters 7 different from device to device. In an attempt to pursuit minuter patterns than the resolution of the material regardless of the flatness of the surface of the solid state imaging device, the color filters 7 are formed with curvature like the pupil as shown in FIG. 33. Consequently, the color filters 7 are overlapped at the edge portions thereof with the adjacent ones, even if flatness on the surface of the solid state imagining devices is made higher. The light traveling through the overlapped parts, therefore, produces irregular image such as mixed color or flickers. Besides, the shape of the surface in the color filters 7, which is curved but not flat, causes the photo spectrography in each of pixels to vary. As a consequence, poor characteristic such as flickers or irregular shading are observed in the solid state imaging device.
The distribution of molecular weight in the natural protein is, even if precisely refined, is hard to be make uniform with high reproducibility. In addition, the natural protein contains an alkali metal such as Na or K of as much as several thousands ppm, which diffuses in the solid state imaging device and increases dark current. Especially in the solid state imaging device, particular pixels with bigger dark current than the surrounding pixels show up as white dots on the picture, which causes white blemish to appear in several weeks after manufacturing the solid state imaging device.
To solve these problems, it is proposed to use a synthetic photosensitive material which have high resolution in Japanese Laid-open publications Nos. 1-142605, 2-96704, 4-163552 and others. According to those publications, synthetic photosensitive materials are synthesized by dissolving a copolymer containing dyeing radicals and a photosensitizer into an organic solvent. According to those methods, color filters are formed by applying the synthetic photosensitive materials, then exposing the materials to ultraviolet rays, and developing the unexposed portions with the organic solvent or a water solution containing the organic solvent as a developer.
In general, if the synthetic photosensitive materials employing the organic solvent are applied to the transparent flattening layers for forming color filters on the surface of the solid state imaging device, transparent flattening layers 6 may be dissolved into the organic solvent so that mixed layers may be formed between the transparent flattening layers 6 and the color filter layers. In this process, after the color filter layers are formed and patterned, it is impossible remove the mixed layers formed in the unexposed areas. Accordingly, when the first of the color filters 7 are formed, the mixed layers experience undesired coloring. Furthermore, when the second or the third color filter 7 are formed, the mixed layers colored during disposition of the first color filters 7 still remain at the interface between the second or the third color filters 7 and transparent flattening layers 6. Accordingly, mixed color appears to invite problems leading to inferior pictures such as flickers.
Speaking the conventional method in more detail, in order to remove the transparent flattening layers 6 mounted on the bonding pads 3 and the scribe line 4, dry etching such as O.sub.2 using oxygen plasma is employed. This method produces more particles than the method of removal through exposure and development techniques. Besides, dark current increase due to plasma damage, which in turns causes white blemish. This method, however, provides extremely higher uniformity in thickness of the layer than the conventional method which uses the material consisting of natural protein and a dichromate. It follows that the shape of the color filters are made considerably uniform. As a consequence, the method of forming the color filters through the use of the synthetic photosensitive materials with the organic solvent, is more and more effective as imaging elements in the solid state imaging device become smaller and smaller, because of its higher degree of controllability on patterns.
Thus, irregular or deformed patterns on the color filters 7 deteriorate the characteristics of the solid state imaging device, whereas the method of using the synthetic photosensitive materials for the color filters may solve the above discussed problems but faces another problem of inferior images caused by flickers, particles, white pecks and the like.
Keeping those problems in mind, the present invention is to provide a solid sate imaging device with excellent imaging performance and characteristics, while meeting the demand for downsizing of chip size and a higher number of pixels in the solid state imagining device.
3. Summary of The Invention
To solve the problems described above, an embodiment of the present invention provides a solid state imaging device which comprises a substrate having at least light receiving sections and charge transfer sections, a transparent gap filler layer and a transparent flattening layer mounted on the substrate and color filters of synthetic photosensitive material on the transparent flattening layers.
To solve the problems described above, another embodiment of the present invention provides a method of manufacturing a solid state imaging device which comprises the steps of: preparing a substrate having at least light receiving sections and charge transfer sections; forming light-shield material on the charge transfer sections; covering the light receiving sections and the charge transfer sections with a protecting layer; forming a transparent gap filler layer of photosensitive thermosetting material on the protecting layer in the light receiving sections; forming a transparent flattening layer of photosensitive thermosetting materials on the transparent gap filler layer and the protecting layer in the charge transfer sections; and forming color filters of synthetic photosensitive material with a water solvent, on the surface of the transparent flattening layers. Preferably, the color filters may be formed through light exposure and development techniques.
To solve the problems described above, still another embodiment of the present invention provides a method of manufacturing a solid state imaging device which comprises the steps of: preparing a substrate having at least light receiving sections and charge transfer sections, said substrate further having bonding pads for external connection of the solid state imaging device and a scribe line for separation of the solid state imaging device into individual solid state imaging units; forming light-shield material on the charge transfer sections; covering the light receiving sections and the charge transfer sections with a protecting layer; forming a transparent gap filler layer of positive type photosensitive thermosetting material on the protecting layer in the light receiving sections; forming a transparent gap filler layer of photosensitive thermosetting material in the scribe line and in the bonding pads; forming a transparent flattening layer of photosensitive thermosetting materials on the transparent gap filler layer and the protecting layer in the charge transfer sections; forming color filters of synthetic photosensitive material with a water solvent, on the surface of the transparent flattening layers; and removing the gap filler layer and the transparent flattening layer from the scribe line and the bonding pads. Preferably, the color filters may be formed through radiation exposure and development techniques. The gap filler layer and the transparent flattening layer in the scribe line and the bonding pads may be removed through radiation exposure and development techniques.
In still another aspect of the present invention, a method of manufacturing a solid state imaging device comprises the steps of: preparing a substrate having at least light receiving sections and charge transfer sections, said substrate further having bonding pads for external connection of the solid state imaging device and a scribe line for separation of the solid state imaging device into individual solid state imaging units; forming light-shield material on the charge transfer sections; covering the light receiving sections and the charge transfer sections with a protecting layer; forming a transparent gap filler layer on the protecting layer in the light receiving sections; forming another gap filler layer of photosensitive thermosetting material in the scribe line and in the bonding pads; forming a transparent flattening layer of non-photosensitive thermosetting materials on the transparent gap filler layer and the protecting layer in the charge transfer sections; carrying out heat treatment on the transparent flattening layer; forming color filters of synthetic photosensitive material with an organic solvent, on the surface of the transparent flattening layers; and removing the gap filler layer in the scribe line and the transparent flattening layer on the bonding pads.
In still another aspect of the present invention, a method of manufacturing a solid state imaging device comprises the steps of: preparing a substrate having at least light receiving sections and charge transfer sections, said substrate further having bonding pads for external connection of the solid state imaging device and a scribe line for separation of the solid state imaging device into individual solid state imaging units; forming light-shield material on the charge transfer sections; covering the light receiving sections and the charge transfer sections with a protecting layer; forming a transparent gap filler layer on the protecting layer in the light receiving sections; forming another gap filler layer in the scribe line and in the bonding pads; forming a transparent flattening layer of negative type thermosetting materials on the gap filler layers and the protecting layer in the charge transfer sections; carrying out heat treatment or radiation exposure or both on the transparent flattening layer; forming color filters of synthetic photosensitive material with an organic solvent, on the surface of the transparent flattening layers; and removing the gap filler layer in the scribe line and the transparent flattening layer on the bonding pads.
The above-mentioned synthetic photosensitive material used in the present invention, contains an extremely few amount of alkali metal in its resins and photosensitizer, so that the material is of higher quality as material for color filters, compared with the conventional material made from the natural protein and the dichromate. The synthetic photosensitive material is remarkably slow in dark reaction, so that change in the characteristics with passage of time is a minimum.
The color filter material of the present invention exhibits an excellent resolution of patterning due to the photosensitizer selected, as compared with the material of the natural protein with the dichromate. Besides, although the synthetic photosensitive material with a water solvent is used to form color filters, the appearance of particles and white blemish caused by plasma damage is suppressed down, because etching method is not used in order to remove the transparent flattening layers formed on surfaces of the bonding pads and the scribe lines.
Consequently, the present invention makes it possible to form color filters with highly uniform shape and spectral characteristics on the finely flattened surface of the semiconductor substrate, while meeting the demand for downsizing and a higher number of pixels in the solid state imaging device.